In a circuit substrate and the like on which an electronic component is mounted, unnecessary radiation (noise) that is emitted from the circuit substrate and the like is required to be reduced. As a device for measuring the unnecessary radiation (noise) that is emitted from the circuit substrate and the like, Japanese Unexamined Patent Application Publication No. 2000-346886 discloses an electromagnetic interference (EMI) measuring device capable of measuring strength of a magnetic field in the three-dimensional direction at a measured point. In the EMI measuring device as described in Japanese Unexamined Patent Application Publication No. 2000-346886, an inclined loop antenna including a ring-like loop part formed on a front end portion, which has a predetermined inclination (54.78°) with respect to the scanning direction, is used as a magnetic field probe.
The EMI measuring device uses the inclined loop antenna having the predetermined inclination so as to measure magnetic fields in the three axial (X-axis, Y-axis, and Z-axis) directions orthogonal to one another. A magnetic field (magnetic flux) intersecting with the loop part of the inclined loop antenna is distributed to the X-axis, Y-axis, and Z-axis uniformly. Therefore, the EMI measuring device can acquire a three-dimensional magnetic field by measuring the magnetic fields while being rotated by 120 degrees each time and combining the results thereof.